Prior processes for treating coal involve removal of moisture and unwanted volatile matter from the coal (typically low-rank coals and lignite) to produce coal of higher quality, with increased heat release per unit mass of fuel. For example, U.S. Pat. Nos. 6,447,559 and 7,879,117 describe processes for producing a clean coal fuel that has a higher heating value per unit mass of coal, compared to the raw coal.
However, these prior processes were not designed to eliminate all volatile matter. A small portion of the volatiles is retained in order to ensure a stable burn of the treated product in coal-fired boilers.
Anthracite coal is relatively scarce compared to bituminous coal and more costly to burn. To date, no one has developed a process to use it as a fuel, less so as a clean fuel. Anthracite coal is a premium variety of coal that is distinguished for its low volatiles content and low moisture. Its properties make it ideally suited for coke and steel manufacturing. Owing to its unique properties, relative scarcity and several other factors, anthracite coal today commands high prices that are multiples of the prices for other coals. Consequently, notwithstanding that its emissions are far cleaner than the emissions from bituminous or what is commonly referred to a brown or steam coal, anthracite coal is not now, nor anytime in the foreseeable future likely to be used as a fuel for industrial boilers.
The ability therefore to upgrade low rank coals and impart to them some of the major characteristics of premium anthracite coal, together with a solution to the problem of the stability of the burn, has not been addressed. The present invention seeks to address this need.